Adults possess a rich set of conceptions about the internal cognitions and mental states of themselves and others. These conceptions constitute a naive theory of mind and as such are crucial to a mature understanding of self and others. But what, if anything, do young children know about the mind? I propose to continue and extend my current research on this question (HD-22149). During the current grant period I have elaborated a theory of children's developing understanding of the mind. This theory sketches the nature of our everyday adult theory of mind, and proposes three phases in the development of this basic understanding: (1) an initial nonmental understanding of human action revolving around a simplified conception of actors' desires, (2) first acquisition of a theory of mind evident in a belief-desire understanding of people, and (3) a major transition from this first mentalism to a later theory evident in older children and adults. In this later transition children move from thinking of the mind as a passive container of mental contents (e.g., holding beliefs) to conceiving of an active interpretive mind. The proposed studies aim to test and elaborate these specific theoretical proposals while more generally advancing our growing understanding of children's knowledge of the mind. A variety of methods -- experimental, and naturalistic -- will be used in order to overcome methodological obstacles to research with young children and to provide a rich set of converging findings on the topics of interest. In all, four series of experiments are proposed. These encompass (1) children's understanding of mental representations, (2) children's understanding of a larger mentalism, including a mentalistic understanding of emotion, (3) children's early and developing understanding of desires, and (4) children's transition from understanding the mind in terms of copies and containers to conceiving of an active interpretive mind.